How to achieve temporary Slow Motion?
All physics have some kind of setting that lets you control the speed at which they're run. This setting can be keyframed or assigned a driver, so for your case, keyframe it to 1.0 at frame 27, then to 0.25 at frame 28 and 63, then 1.0 again at frame 64.
If you want it to gradually slow down and speed up, set something like for example 1.0 at frame 20, 0.25 at frame 28 and 63 and 1.0 again at frame 70.
With particles it's set as the time between frames instead, but the idea is the same. I'll come to that.

For Rigid Body physics, this is located under Rigid Body World in the scene properties. This affects all rigid bodies in the scene.



For Soft Body physics and Cloth simulation, it's set in the physics properties per object.





For Smoke simulation, it's set in the physics properties for the domain.



Fluid simulation is a bit special, as it runs over the entire range of frames being rendered.
The Start value defines what point in the simulation will happen at frame 1. The part of the sim that comes before this time has to be calculated, but gets discarded.
The End value defines what point in the simulation will happen at the last frame.
As an example, let's say you have a 10 second animation, and you want the whole fluid sim to run at one quarter speed, just set start to 0.0 and end to 2.5. These 2.5 seconds will be stretched to take the 10 seconds of your animation.
The Speed value speeds up or slows down like for the other simulation types.
These are set in the physics properties for the domain.



For Particles, as I mentioned before, the setting controls the time between frames rather than a speed factor. To slow down, decrease the Timestep value, to speed up, increase it. To keep the accuracy, you may want to increase the Subframes value, to do calculations in between actual frames.
It's set in the particle settings per set of particle settings. One set of particle settings can be used by several particle systems.